1. Field of the Invention
The invention relates to fuel injectors and more particularly to the assembly of parts of a solenoid-operated control valve in a fuel injector.
2. Description of the Related Art
In a typical fuel injection system, a control valve is disposed between the high pressure side of a fuel passage connected to a pump or compressor, and the low pressure side connected to a reservoir. When the control valve is open, fuel flow from the pump bypasses the injector, “spilling” to the low-pressure reservoir. Fuel injection events are triggered when the control valve is closed, which normally occurs electronically by energizing a solenoid to move an armature mounted to a valve needle.
In a common control valve configuration, the armature is a flat metal plate and the valve needle is a spool or pin. The armature is mounted to the end of the valve needle and moves in a magnetic field generated when the solenoid is energized, thereby closing the control valve.
It is known to mount the armature to the valve needle by bolting as shown, for example, in EP 0 588 475. It is also known to swage the armature to the valve needle as disclosed, for example, in commonly owned U.S. Pat. No. 5,937,520. In the '520 patent, the swaging occurs in another operation separate from assembly, and with time consuming, costly secondary machining and grinding operations.
In some fuel injection systems, particularly common rail systems used in some automobiles, there is not enough space to permit assembling the armature to the valve needle before installing the valve needle in the valve body. Moreover, tight tolerances and small spaces do not permit assembly of the armature to the valve needle by bolting or any other known conventional means. There remains a need to provide assembly of the armature to the valve needle in a manner that will enable a large retention force (retaining the armature on the pin in the face of high acceleration and high fuel pressure), yet permit precise interferences in a small space.